1. Field of the Invention
The present invention relates to a thin film magnetic head assembly and a method of manufacturing the same. According to the invention, the thin film magnetic head assembly includes both a wafer type and a bar type. In the wafer type thin film magnetic head assembly, a substrate is a wafer and a plurality of thin film magnetic head elements are arranged in matrix on the substrate. In the bar type thin film magnetic head assembly, a substrate is formed by a bar and a plurality of thin film magnetic heads are aligned in a longitudinal direction of the bar. The bar type thin film magnetic head assembly may be obtained by cutting the wafer type thin film magnetic head assembly.
2. Description of the Related Art
In a thin film magnetic head having a reading element constituted by a magnetoresistive element such as spin valve film or ferromagnetic tunnel junction element, the magnetoresistive element and its electrode films are embedded in an insulating film made of alumina, and first and second shield films are provided on respective sides of the insulating film. In this structure, when damage or dielectric breakdown occurs in the insulating film provided between the electrode films and the first or second shield film, there might be generated large electric noise, and an electromagnetic conversion property might be degraded.
Japanese Patent Application Laid-open Publications, Kokai Hei 8-293108, Kokai Sho 61-7714 and Kokai Hei 8-167123 and U.S. Pat. No. 5,805,390 have proposed techniques for reducing the degradation of the insulating property and avoiding the dielectric breakdown.
In the Kokai Hei 8-293108, during a wafer process in which various processes are conducted without cutting or dividing a wafer, an electric connection between the electrode films and shield films is maintained, and after the wafer process, this electrical connection is cut off. However, during the wafer process, an electrical insulating property between the electrode films and the shield films could not be measured, and therefore after cutting the wafer or bar into respective thin film magnetic heads, the measurement of the insulating property. One could not know a possible degradation of insulating property or dielectric breakdown which might be generated during the wafer process. Then, a manufacturing yield is decreased, and it is necessary to measure the insulating property for individual thin film magnetic heads. It is apparent that such a checking work is very cumbersome.
In the Kokai Sho 61-7714, there is disclosed a magnetoresistive type thin film magnetic head in which upper and lower shield films are electrically connected to each other to keep these shield films equipotential, and no electrostatic charge is stored during the operation. However, in this known magnetoresistive type thin film magnetic head, insulating property of an insulating film sandwiched between the shield film and an electrode film could not be measured, and therefore manufacturing yield is low.
In the Kokai Hei 8-167123, upon manufacturing a magnetoresistive type thin film magnetic head, upper and lower shield films, electrode films and a magnetoresistive element film are connected to each other during the wafer process, and they are separated from each other after the wafer process. However, also in this known magnetoresistive type thin film magnetic head, insulating property of an insulating film between a shield film and an electrode film could not be measured, and thus sufficiently high manufacturing yield could not be attained.
Furthermore, in the U.S. Pat. No. 5,805,390, in order to protect a MR element against the dielectric breakdown during a time period from the formation of the MR element to the installation of a MR head onto a recording and reproducing device, upper and lower shield films are short-circuited during the wafer process, and after the wafer process, upper and lower shields are connected to each other via a resistor. In this known technique, a manufacturing process becomes rather complicated and manufacturing cost is increased owing to the reason that the upper and lower shields have to be short-circuited not only during the wafer process but also after the wafer process.
The present invention has for its object to provide a thin film magnetic head assembly as well as a method of manufacturing the same, in which degradation or dielectric breakage of the insulating films provided between the shield films and electrode films can be effectively prevented during the manufacturing process.
It is another object of the invention to provide a thin film magnetic head assembly as well as a method of manufacturing the same, in which an insulating property of insulating films between shield films and electrode films can be measured.
It is still another object of the invention to provide a thin film magnetic head assembly and a method of manufacturing the same, in which shield films and electrode films can be isolated without injuring the shield films.
According to the invention, a thin film magnetic head assembly includes a substrate and a plurality of thin film magnetic head elements provided on the substrate, wherein each of said thin film magnetic head element comprises:
a first shield film formed to be supported by said substrate;
a first insulating film formed on said first shield film:
a magnetoresistive element formed on the first insulating film;
first and second electrode films formed on said first insulating film to be connected to respective end portions of the magnetoresistive element;
a second insulating film formed to cover said magnetoresistive element as well as said first and second electrode films;
a second shield film formed on said second insulating film; and
a conductive film formed on said first insulating film such that the conductive film extends outside said second shield film viewed in a film stacking direction and is connected to at least one of said first and second electrode films as well as to at least one of said first and second shield films.
In the thin film magnetic head assembly according to the invention, in each of the thin film magnetic head elements, the first insulating film is formed on the first shield film and the magnetoresistive element and first and second electrode films are formed on the first insulating film, and thus the magnetoresistive element and first and second electrode films are shielded by the first shield film when the substrate is divided into respective thin film magnetic heads. Furthermore, since the first and second electrode films and magnetoresistive element are covered with the second insulating film and second insulating film is covered with the second shield film, the magnetoresistive element and first and second electrode films are shielded also by the second shield film.
Each of a plurality of the thin film magnetic head elements of the thin film magnetic head assembly according to the invention includes the conductive film. This conductive film is provided on the first insulating film to extend outside at least of the second shield film among the first and second shield films and is electrically connected to at least one of the first and second electrode films as well as to at least one of the first and second shield films. For the sake of simplicity, now a case in which the conductive film is connected to the first electrode film and second shield film will be explained. In this case, the first electrode film becomes equipotential with the second shield film, and the second electrode film becomes equipotential with the first electrode film via the second shield film, and thus the second electrode film becomes equipotential with the second shield film. Therefore, during the wafer process, no voltage is applied across the second insulating film provided between the first and second electrode films and the second shield film. In this manner, the second insulating film can be prevented from being damaged or broken due to the electrostatic charge.
When the conductive film is electrically connected to the first electrode film and first shield film, the first and second electrode films become equipotential with the first shield film. Therefore, no voltage is applied across the first insulating film provided between the first and second electrode films and the first shield film during the wafer process, and therefore the first insulating film can be protected against damage or dielectric breakdown.
In a preferable embodiment of the thin film magnetic head assembly according to the invention, said conductive film is connected both to the first and second electrode films and to the first and second shield films. In-this case, during the wafer process, no voltage is applied across the first insulating film provided between the first and second electrode films and the first shield film as well as across the second insulating film provided between the first and second electrode films and the second shield film, both the first and second insulating films can be protected against damaged or dielectric breakdown.
In another preferable embodiment of the thin film magnetic head assembly according to the invention, said conductive film is electrically connected both to the first and second electrode films. In this case, the magnetoresistive element is short-circuited by means of the first and second electrode films and conductive film, and therefore the magnetoresistive element can be protected.
The structure in which the conductive film is electrically connected both to the first and second electrode films can provide not only the above mentioned merits for the thin film magnetic head assembly, but also extremely high utility for the method of manufacturing the thin film magnetic head assembly. That is to say, by cutting the conductive film, the first or second electrode film can be electrically separated from the first or second shield film. After this cutting process, the insulating property of the insulating film can be measured. The above mentioned cutting operation and the measurement of the insulating property may be performed on the wafer or bar. Therefore, the measurement of the insulating property can be carried out very easily.
As explained above, the conductive film extends outside at least the second shield film viewed in the film stacking direction. Therefore, the conductive film can be cut at an area where the second shield film is not influenced by the cutting operation. Therefore, a generation of conductive material debris caused by cutting the conductive film can be prevented, and thus a short-circuit between the second electrode film and the second shield film caused by adhesion of conductive material debris onto cut surfaces of these films can be also prevented. It is preferable to form the conductive film to extends outside both the first and second shield films. In this structure, the conductive film can be cut at an area at which both the first and second shield films are not existent.
In another preferable embodiment of the thin film magnetic head assembly according to the invention, each of the thin film magnetic head elements includes a third insulating film, a first terminal conductor, a second terminal conductor and a third terminal conductor. Said third insulating film constitutes an outermost layer of the thin film magnetic head. Said first terminal conductor is electrically connected to said second shield film and is covered with said third insulating film. Said second terminal conductor is electrically connected to said first electrode film and is covered with said third insulating film. Said third terminal conductor is electrically connected to said second electrode film and is covered with said third insulating film.
In this thin film magnetic head assembly, end surfaces of said first, second and third terminal conductors may be exposed in the surface of the third insulating film by, for instance, polishing. Then, the insulating property of a number of thin film magnetic head elements can be measured simultaneously by contacting an probe array having an arrangement pattern corresponding to that of the first to third terminal conductors to the exposed end surfaces of these terminal conductors.
After cutting the conductive film and measuring the insulating property, the thin film magnetic head assembly may include an electrically conductive paste layer. This conductive paste layer may be applied on the surface of the third insulating film and the end surfaces of the first, second and third terminal conductors such that the first, second and third terminal conductors are electrically connected to each other.
In such an embodiment of the thin film magnetic head assembly, the first and second terminal conductors connected to the first and second electrode films are electrically connected to the third terminal conductor connected to the first and second shield films by means of the conductive paste layer. Therefore, the first and second electrode films can be kept equipotential with the first and second shield films. Then, the first insulating film and magnetoresistive element can be prevented from being broken due to the electrostatic charge during a process after the measurement of the insulating property.
In another embodiment of the thin film magnetic head assembly according to the invention, each of the thin film magnetic head elements includes at least one metal film provided on the first insulating film at a position corresponding to a middle portion of the conductive film, and is covered with said third insulating film.
Upon manufacturing such a thin film magnetic head assembly, said third insulating film is ground or polished to expose an end surface of said metal film, and then the metal film is removed by etching. After that, said conductive film is cut at its middle potion through a hole formed by removing the metal film.
Furthermore, as an addition step, after cutting the conductive film at its middle portion, an insulating resistance of the first or second insulating film may be measured across the first terminal conductor and at least one of the second and third terminal conductors. In this manner, the insulating property of the first or second insulating film can be measured.